DK148963B - COATING MATERIALS FOR CORROSION PROTECTION OF METAL GOODS, CONTAINING SALTS OF NITROPHTHAL ACIDS - Google Patents

Description

148963 i

The invention relates to a coating material for corrosion protection of metal objects, especially of iron, of the kind specified in the preamble to the claim.

In addition to the long-known corrosion protection agents based on lead ammonia, strontium chromate, lead silicochromat, zinc potassium chromate, zinc phosphate and lead phosphite, the use of corrosion protection agents containing salt of organic acids has also recently been proposed. The corrosion protection agents disclosed in German Patent No. 2,204,985 contain e.g. zinc and / or lead salts of nitrophthalic acids. These nitrophthalic acids are understood to mean 3- and 4-nitrophthalic acids as well as a mixture of the indicated isomers and di-nitrophthalic acids.

While these corrosion protection agents have substantially better activity relative to corrosion protection agents on the basis of the usual pigments, however, they exhibit drawbacks which discourage their use despite their good anti-corrosion effect. Namely, it was occasionally found that the lacquer film in these corrosion protection agents tends to blister, which leads to the risk of destruction of the lacquer film. The occasional occurrence of a blistering formation probably lies in the fact that the nitrophthalic acids used cannot generally be obtained at affordable prices in sufficiently pure form, which is why frequently cheaper, more impure products are used.

It is an object of the invention to provide a coating material for corrosion protection, of the kind specified in the preamble to the claim, which exhibits not only a high corrosion protection value, but also a sufficiently high mechanical strength, but which in particular does not tend to blister.

It has now been found that corrosion protection coatings containing nitrophthalic acid salts exhibit the desired properties when they contain, according to the invention, zinc salts of 5-nitroisophthalic acid or of mono-nitro terephthalic acids or mixtures thereof.

The coating material according to the invention, which is of the kind specified in the preamble of the claim, is peculiar to that of the characterizing part of the claim.

These corrosion protection coating materials exhibit, on average, a higher corrosion protection value than the previously mentioned corrosion protection coating materials containing salts of nitrophthalic acids. Also, the poorer solubility of the salts found in the corrosion protection coatings of the invention over the salts used in connection with the previously known corrosion protection coatings has a favorable effect on the durability of the protective lacquer film.

This favorable relationship with the corrosion protection coating materials of the invention could not be foreseen because a relationship between the structure of the orthophthalic and terephthalic acid orthophthalic acids used for the known corrosion protection coatings used, which refers to such diverse behavior, was not known.

In the following table, various known corrosion protection agents (Examples 1 to 4) are contrasted with the corrosion protection agents of the invention (Examples 5 to 8), indicating their composition and their corrosion protection value.

In all examples, a binder based on Alftalat AM 380 from Bayer AG was used, which is an air-drying binder based on flax oil / wood oil alkyd resin.

148963 4

Known technique according to the invention

Ingredients 1 2 3 4__5 6 7_8--

Alkyd resin 25 25 25 25 25 25 25 25

Solvent 27 29 29 29 29 29 29 29

Titanium Dioxide 14 10.9 11 12 11 12 9.5 10.8

Microtalkum 16 16 16 16 16 16 16 16

Tungspat 16 18 18 18 18 18 18 18

Zinc potassium chromate (according to DIN 55 902) 2.0

Nitrophthalic acid lead (according to patent 2,204,985 1,2

Nitrophthalic acid zinc (according to patent 2,204,985) 2.0 1.0 5-nitroisophthalic acid zinc made from 1 mole of acid and

3 moles ZnO 2.0 1.0 J

Nitroterephthalic acid zinc, j made of 1 mole of acid and 3 moles of ZnO ________ 2.5 1.0

Corrosion-! protection value (») 31 71 64 52 71 64 70 64 148963 5

By comparing Example 5 (the invention) with Example 3 (prior art), it is seen that using the same amount of metal salt can achieve a higher corrosion protection value (71) according to the invention than with prior art (64).

By comparing Example 6 (the invention) with Example 3 (prior art), it is seen that using the half amount of metal salt, the same corrosion protection value (64) of the invention can be obtained as in the prior art.

Similar conclusions can be drawn by comparing the embodiments of Examples 7 and 8 (according to the invention) with Example 3 (prior art).

If in each case the corrosion protection values of the corrosion protection agents according to the invention listed in the table in relation to the known corrosion protection agents show only slight differences (cf. on the one hand examples 5 and 7 corresponding to the invention and on the other example 2 corresponding to known technique), the superiority of the corrosion protection agents of the invention shows that, as a cation, they at all use only less salient zinc for physiological effects.

In the case of oven-drying alkyd resin-melamine resin binders, similar results were found in the corrosion protection test.

The corrosion protection test was carried out taking into account certain application technical parameters which ensure reproducibility, such as as stated in the journal "Farbe und Lack", Volume 75 (1969, p. 945).